1. Field of the Invention
The present invention relates to image processing in digital color copiers. More specifically, the present invention relates to image processing to discriminate whether input image data is character data or non-character image data by performing block selection and performing an image process on the character data.
2. Description of the Related Art
Copy machines contain an image processing unit that includes a scanner which scans an input image. When the input image is scanned, the conventional processing unit detects, on a pixel-by-pixel basis, whether input data is text or a continuous tone image by detecting edges of text objects as well as the color of the text objects. The image processing unit then applies an appropriate image process to the contents of the input image based on the type of image data detected. For example, if black text is detected, the edge detection process may result in application of an edge enhancement process that applies only black toner in order to sharpen the output image by making the edge clearer. If a continuous tone image area is detected, a smoothing process may be applied to smooth the rich colored output image.
However, such conventional image processes have drawbacks in that, since the color and edge detection processes are performed on a pixel-by-pixel basis, it is not easy to detect the color of text objects. For instance, the edge portion of a text object is generally neither black nor white in detail, but rather, generally appears to have some chroma, i.e. it looks like a colored pixel. Thus, some black text objects may be misjudged as being non-black. In order to address this misjudgment, conventional systems apply a threshold test for determining whether or not an object is black. The threshold value can be adjusted to reduce the misjudgment, depending on the precision of the scanner. However, one drawback with this technique is that low saturation colored text is often detected as black text.
Another drawback of performing the processing on a pixel-by-pixel basis is that the image processing unit generally assumes that dark colors are foreground colors and light colors are background. However, where the text is actually white with a dark background color, conventional copiers have trouble performing text detection.
Additionally, in performing the image processing, conventional copiers provide pre-set functions for a user to select the type of original document being scanned so as to set a type of image recognition process to be used in scanning the input image. That is, based on the pre-set function selected, the image recognition process will be pre-set to detect text only, continuous tone images, or a combination of both, thereby reducing misjudgment of text and non-text data during the detection process. However, the conventional functions generally result in enabling or disabling text detection, preparing appropriate parameters for text detection, preparing appropriate parameters of an image filter and RGB to CMYK conversion, and selecting printout resolution which are not conducive for performing image processing by block selection.